Means for gas-flushing metal melts

ABSTRACT

A molten metal in a container is treated with a gas. The gas is supplied through an opening, preferably a slit-shaped opening, in the bottom or lower wall portion of the container, thus forming bubbles which ascend in the molten metal. The container is rotated or shaken or vibrated so that a flow is created in the molten metal relative to the wall of the container. The molten metal thus passing by the gas supply opening removes the gas bubbles from the gas supply opening before the bubbles have had time to grow to the size they would have reached in stagnant molten metal.

United States Patent [72] lnventors Erik Anders Ake Josefsson;

Lars Gosta Almhed, both of Borlange, Sweden 211 App]. No. 831,283 [22] Filed June 6, 1969 [45] Patented Jan. 11, 1972 [73] Assignee Stora Kopparbergs Bergslags Aktiebolag Falun, Sweden [54] MEANS FOR GAS-FLUSHING METAL MELTS 7 Claims, 3 Drawing Figs.

52 US. Cl 266/34 A, 75/59, 266/34 PP [51] Int.Cl C2lc 7/00 [50] Field of Search 266/34 R,

34 A, 34 T, 34 PP, 36 R; 75/59, 60

[5 6] References Cited UNITED STATES PATENTS 2,599,158 6/1952 Brassert 75/60 2,855,293 10/1958 Savard et a1.. 75/60 Primary Examiner-Gerald A. Dost Attorney-McGlew and Toren ABSTRACT: A molten metal in a container is treated with a gas. The gas is supplied through an opening, preferably a slitshaped opening, in the bottom or lower wall portion of the container, thus forming bubbles which ascend in the molten metal. The container is rotated or shaken or vibrated so that a flow is created in the molten metal relative to the wall of the container. The molten metal thus passing by the gas supply opening removesthe gas bubbles from the gas supply opening before the bubbles have had time to grow to the size they would have reached in stagnant molten metal.

PATENTED JAN] 1 1972. 316333398 3 i8 19 INVENTORS ERIK A-A. JOSEFSSON LARS G. ALMHED MEANS FOR GAS-FLUSHING METAL MELTS In order to remove dissolved gases or gaseous reaction products from metal melts, particularly steel melts, so-called gas flushing is often used, that is, a gas which in itself does not react, or reacts only very slightly with the melt, is supplied to the bottom part of the container or furnace where the molten metal is situated. The bubbles of flushing gas supplied which thus rise through the melt can then absorb gases dissolved in the melt, which thus rise with the bubbles to the surface of the melt and are removed from the melt. Since the partial pressure for the dissolved gases is initially zero in the flushing-gas bubbles, the dissolved gases diffuse even at low percentages into the bubbles, and an extremely thorough degassing can thus take place, assuming that there is a sufficiently large contact surface between the flushing gas and the melt so that a sufficient quantity of dissolved gas can pass the boundary between metal and gas and enter the bubble while it is rising in the melt. The quantity of dissolved gas which can be removed from the melt by a certain quantity of flushing gas is thus dependent on the contact surface per volume unit and thus on the bubble size; the smaller the bubbles are, the more can their percentage of dissolved gas during the rising process approach equilibrium, and the greater the quantity of dissolved gas which can be removed.

Even if the gas is supplied through narrow channels, for example with the help of porous ceramic parts in the walls of the furnace or container, the rising bubbles will be relatively large in relation to the cross-sectional dimension of a channel, partly due to the fact that the bubbles do not leave the ceramic wall near the opening of the channel or pore until they have become relatively large. There is also the tendency of the bubbles from adjacent channels to join to form larger bubbles when the gas is supplied through porous stones.

The present invention aims at achieving a more effective distribution of the flushing gas, and thus making better use of this, by combining flushing according to the known method with a mechanically effected relative movement in the melt so that this moves along the walls of the furnace or container, in which channels or pores for the supply of flushing gas are arranged substantially perpendicularly to the direction in which the gas flows out from said channels or pores. In this way the gas bubbles are continuously brushed off the points where they form near the opening of the supply channel and are removed before they have had time to become noticeably larger than the dimension determined by the width of the channel.

The relative movement of the melt can be effected in many different ways, by mechanical stirring, by means of an electromagnetic field, by means of the supply of impulses with gas, etc., but in order to be efficient the speed of the melt should be greater than or at least of the same order of magnitude as the rate at which the gas is supplied at the opening of the supply channel, that is in the order of magnitude of l m./sec. It has been found particularly suitable to use a movement achieved by rotation of the furnace or container in order to attain this high speed or the melt. 1n the first place a so-called vibratory or shaking ladle has been found particularly suitable. ln such a ladle the movement of the melt is developed by a substantially cylindrical container or ladle containing the melt, which is made to rotate about a vertical or substantially vertical axis with frequent changes in the direction of rotation, or by making the axis of the container describe a cylinder, cone or double-cone or similar figure, or a pendulum movement in the plane, or a combination of one or more of these movements.

Such vibratory ladles have been described, inter alia, in Swedish Pat. No. 173,423, German Pat. No. 1,142,061 and Belgian Pat. No. 648,646.

in accordance with the invention a gas supply means with gas-distributing channels is applied in such a vibratory ladle through the part of the lining which forms the bottom of the ladle, or the part of the ladle wall which is covered by the melt. The gas is supplied through a tube to a gas-distributing insert in the wall of the lining; the insert may consist of porous elements or ceramic material or of a number of tubular channels in the lining material. For the combination with the mechanical movement of the melt, however, it is particularly favorable to arrange the gas supply so that the bubbles are distributed along a considerable length on a line perpendicular to the direction of movement of the melt. This is achieved by placing the supply channels in a row across the direction of movement of the melt, or by placing two elements of, for example magnesite brick, in the wall which form a gap between them through which gas can pass. The elements are inserted so that the opening of the gap forms a right angle or obtuse angle with the direction of flow attained by the melt during the vibratory movement. The width of the gap should be in the order of 1 mm. in order to enable the supply of considerable quantities of the flushing gas per time unit while maintaining the fine distribution, a series of gaps may be arranged successively which the melt passes during its circulation. The gas flow is regulated in the normal manner by a regulating device inserted in the supply conduit.

in order to further explain the invention, a preferred embodiment will be described with reference to the accompanying drawing.

FIGS. 1 and 2 show in a side view and a top view, respectively, a vibratory ladle of a type known per se which has been modified in accordance with the present invention, and

FIG. 3 shows a top view of another arrangement of the bottom of the ladle.

The vibratory ladle comprises a ladle or container 1 for the molten metal to be treated. The ladle is tiltably pivoted on two pegs 2 and 3 in a substantially horseshoe-shaped support 4, which is pivoted on pegs on three crankshafts or eccentric shafts 5, 6 and 7. The eccentric shaft 7 is rotated by means of an electric motor 8, the others being freely movable, thus giving the ladle the desired vibratory movement. The support 4 is open between the pivoting points of the eccentric shafts 5 and 6, and therefore the ladle can be tilted about its pivoting pegs 2 and 3. For the tilting of the ladle the shaft 2 is provided with a gear ring 9 which can be turned by means of a gear wheel 11 arranged on a shaft 10. In order to turn the shaft 10 an electric motor or the like can be arranged. This is not shown in the drawings, however.

A locking means 12 is also indicated in the drawings, to lock the tilting movement of the ladle.

In accordance with the invention the ladle 1 is provided at the bottom with a gas-distributing insert 13 consisting of two elements 14 and 15 forming a gap 16 between them. As seen in FIG. 1, the elements 14 and 15 should preferably be somewhat conical so that they do not become detached and blown into the melt. In FIG. 3 a plurality of radially extending gaps or slits 16 are shown in the bottom of the ladle l.

The flushing gas is supplied to the gap 16 via a bowl-shaped metal ferrule 17 which ensures that the gas does not leak out under the refractory lining of the ladle. The flushing gas is supplied to the metal ferrule through a conduit 18 which is made partially of flexible material so that it does not obstruct tilting of the ladle. A regulating device 19 is arranged in the conduit 18 to control the supply of gas.

The vibration of the ladle results in the molten metal being brought into a rotary motion relative to the ladle. The molten metal close to the bottom of the ladle will, therefore, flow in a direction perpendicular to the gap 16.

The vibratory movement not only contributes to decreasing the size of the bubbles in the gas supplied, it also ensures a uniform distribution of these bubbles in the entire metal melt.

However, in certain cases it may be necessary to limit the speed of the vibratory movement so that the mixing movement between slag and metal is avoided which occurs at so-called over critical speed, or to avoid a direct contact between the metal melt and the atmosphere above the furnace, which is also the result of a high speed of rotation.

EXAMPLES OF APPLICATION 1. In a vibratory ladle according to FIG. 1 molten steel was treated for the removal of carbon and oxygen with argon gas supplied in accordance with the invention. Before the treatment the carbon content in the melt was 0.05 percent and its oxygen content 0.07 percent. By flushing argon gas through the melt, the vibratory device being driven at a speed for the eccentric movement of 30 r.p.m., these percentages were decreased to 0.0.25 percent and 0.03 percent, respectively.

2. In the same vibratory ladle stainless steel was treated. After having been blown with oxygen the melt reached a composition of 17.5 percent Cr., 0.15 percent C. With the help of the means according to the invention the melt was supplied with 6 mP/ton ofa gas mixture consisting of argon and oxygen, the percentage of oxygen gas in the gas mixture being at the start held at 50 percent and decreasing continuously during the treatment to nearly zero. The total quantity of argon supplied was 4.5 'Nm. /ton, the quantity of oxygen gas 1.5 Nmfilton. After the treatment the carbon content of the melt was 0.03 percent whereas the chromium content was maintained at 17.5 percent, thanks to the continuously decreasing oxygen content in the flushing gas.

Particularly when refining iron melts with a high chromium content, the supply of flushing gas according to the invention may have a favorable effect even while oxygen gas is being blown onto the surface of the melt from above.

We claim:

1. Apparatus for carrying out gas flushing of metal melts comprising a so-called vibratory or shaking ladle of conventional design including a substantially cylindrical container having a vertical axis, means for suspending said container for imparting to the liquid metal in the container a circular motion by making the axis of the container describe at least one of a cylindrical, conical, double conical, and pendulum movements and the combination of such movements, said container having at least one elongated gas-distributing slit in its bottom lining and said slit extending substantially radially in relationship to the axis of rotation of said container.

2. Apparatus, as set forth in claim 1, wherein the width of said elongated gas-distributing slit is in the order of magnitude of 1 mm.

3. Apparatus, as set forth in claim 1, wherein two lining elements being arranged in the bottom of said ladle and being spaced from each other for forming said gas-distributing slit.

4. Apparatus, as set forth in claim 1, wherein at least one porous insert of ceramic material is arranged between said two lining elements in the bottom of said ladle for forming said gas-distributing slit.

5. Apparatus, as set forth in claim I, wherein a plurality of said slits extend substantially radially in the bottom lining of said container.

6. An apparatus for treating a molten metal with a gas comprises a container having a substantially circular cross section, said container having an opening in the upper portion thereof for the supply of molten metal into said container, the bottom wall of said container having at least one elongated slitlike opening therein with the slitlike opening extending radially relative to the axis of said container for the supplying gas thereto, means for shaking said container so as to effect a motion of the molten metal relative to the walls of said container and thus producing a flow of molten metal past said gas supply opening, and means for tilting the container so as to discharge the molten metal after having been treated with the gas.

7. An apparatus as claimed in claim 6, in which the means for shaking the container is arranged to give the container a circular motion. 

2. Apparatus, as set forth in claim 1, wherein the width of said elongated gas-distributing slit is in the order of magnitude of 1 mm.
 3. Apparatus, as set forth in claim 1, wherein two lining elements being arranged in the bottom of said ladle and being spaced from each other for forming said gas-distributing slit.
 4. Apparatus, as set forth in claim 1, wherein at least one porous insert of ceramic material is arranged between said two lining elements in the bottom of said ladle for forming said gas-distributing slit.
 5. Apparatus, as set forth in claim 1, wherein a plurality of said slits extend substantially radially in the bottom lining of said container.
 6. An apparatus for treating a molten metal with a gas comprises a container having a substantially circular cross section, said container having an opening in the upper portion thereof for the supply of molten metal into said container, the bottom wall of said container having at least one elongated slitlike opening therein with the slitlike opening extending radially relative to the axis of said container for the supplying gas thereto, means for shaking said container so as to effect a motion of the molten metal relative to the walls of said container and thus producing a flow of molten metal past said gas supply opening, and means for tilting the container so as to discharge the molten metal after having been treated with the gas.
 7. An apparatus as claimed in claim 6, in which the means for shaking the container is arranged to give the container a circular motion. 